Present data suggest that the glycosyl moieties of glycoproteins are involved in the cellular and moleculr interactions which take place in developing and adult defined system of clinical importance, in which the functions of cell-surface and extracellular glycoproteins in the differentiation an interactions of characterized single cells can be assessed quantitatively by biochemical, serological, genetic and functional criteria. The biosynthesis and cell-type oforigin of glycosaminoglycans glycopeptides, and intact glycoproteins will be studied throughout thymus development and involution. Using organ culture technology together with specific inhibitors (tunicamycin, sulfate deprivation, selenate substitution), mutant mice, or stimulators (B-Xylosides) of glycosylation, the involvement of glycosyl moieties in the morphological, serological, functional and biochemical development of the thymus and thymocytes will be investigated. Similarly, the involvement of asparagine-linked glycosyl moieties in mature T cell mediated cellular-interactions (mixed lymphocyte reactions, T cell cytotoxicity, T cell suppressor functions and T cell helper functions) will be determined. Also, the role of these glycosyl moieties in lymphocyte homing will be investigated. The effects of oxogenously added glycopeptides (derived from thymocytes or stimulator cells) on T cell mediated cellular interactions will be determined, subsequently active glycopeptides will be structurally characterized. The relationship between thymic epithelial morphogenesis and thymocyte cytodifferentiation, and the influences of the thymic mesenchyme on these events will be explored. The results of these studies will increase our understanding of the functional rolls of glycosyl moieties on glycoproteins, in general, and will prove or disprove the involvement of these glycosyl moieties in specific T cell mediated interaction and thymus development.